Saudi Arabia has closed its borders with Yemen to prevent the spread of Rift Valley Fever, which has left dozens dead and hundreds ill in both countries, a Saudi official said Monday.

Yemen's ambassador to Riyadh said he could not confirm the closure. "I know nothing about it," Mohammed Kabab told AFP.

The Saudi health ministry said Monday that 27 people in Saudi Arabia have died of the fever out of a total of 129 who have been stricken with the disease.

The Jizan region was the worst affected with 105 people contaminated, the ministry said.

Saudi King Fahd ordered on Sunday the destruction of all livestock carrying or suspected of carrying the deadly fever.

The fever was first reported on September 11 in the south of the kingdom near the border with Yemen, where 30 people have since died of the disease in the Red Sea region of Hodeida, 225 kilometers (140 miles) west of Sanaa.

Saudi and Yemeni authorities, meanwhile, are boosting cooperation in their attempts to eradicate the fever.

Twenty Saudi planes sprayed insecticides in the infected zones on both sides of the Saudi-Yemeni border, while the two countries have met to establish joint technical committees, official sources said.

International assistance has also been forthcoming: South African experts arrived in Saudi Arabia Sunday, while Yemen said teams from the Geneva-based World Health Organization (WHO) and the US-based Center for Disease Control (CDC) arrived Monday in Sanaa.

The WHO and CDC teams are to collect samples from the contaminated regions to analyze them in CDC laboratories in Cairo and South Africa, the Yemeni news agency SABA said.

It is the first time that the disease, which affects domestic animals and can be transmitted to humans by mosquitoes, has been known to strike outside Africa.

Symptoms include hemorrhagic fever, encephalitis and eye problems, although human deaths from the disease are rare, according to experts – RIYADH (AFP)